Bimetal snap switch with disconnect lever to prevent contacts from permanently welding



Dec. 19, 1967 C. A. LANDlN 3,359,389,, BIMETAL SNAP SWITCH WITH DISCONNECT LEVER TO PREVENT CONTACTS FROM PERMANENTLY WELDING Filed Feb. 18, 1966 Z! 56 gg INVENTOR.

CARL A. LANDIN BYW,

ATTOR NEYS United States Patent 3,359,389 BIMETAL SNAP SWITCH WITH DISCONNECT LEVER TO PREVENT CONTACTS FROM PER- MANENTLY WELDING Carl A. Landin, West Hartford, Conn., assignor to The Hart Manufacturing Company, Hartford, Conn., a corporation of Connecticut Filed Feb. 18, 1966, Ser. No. 528,648 Claims. (Cl. 200-438) ABSTRACT OF THE DISCLOSURE The device of this invention comprises a support having a fixed contact secured thereto, a switch arm mounted on the support and carrying a second contact for movement relative to said fixed contact, a bimetallic member and a disconnect lever cantilever supported on the support with the disconnect lever positioned in spaced aligned relation between the switch arm and the bimetallic member, the latter having a free end portion movable into a first position for applying an initial force to the switch arm remote from its contact to move it away from the fixed contact, and the disconnect lever having a free end portion engageable with that of the bimetallic member upon continued movement thereof beyond said first position for applying an additional contact opening force to ensure opening the contacts when they fail to break responsive to said initial force applied to the switch arm.

This invention relates to switches for controlling electrical circuits and particularly concerns snap switches of the type having a heater controlled bimetallic actuator.

A principal object of the invention is to provide an improved snap switch of the above described type which effects a quick, chatter-free switching action and which is particularly suited to significantly increase the likelihood of contact opening even when the contacts are sticking thereby to prevent them from being permanently welded together by electrical overheating.

Another object of the invention is to provide such a switch which may be quickly and easily adjusted for different operating conditions and which may be readily manufactured and assembled at low cost to provide a compact durable switch unit.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereafter set forth, and the scope of the application of which will be indicated in the appended claims.

In the drawing:

FIG. 1 is a side elevational view, partly in section and partly broken away, showing a preferred embodiment of a switch constructed in accordance with the invention;

FIG. 2 is a side elevational view, partly broken away, showing a bimetallic actuator in a first deflected position for opening switch contacts under normal conditions;

FIG. 3 is a view similar to FIG. 2 showing the bimetallic actuator in a further deflected position for opening switch contacts which had been sticking together; and

FIG. 4 is an end view of the switch of FIG. 1.

Referring now to the drawing in detail, a preferred embodiment of a switch is illustrated as having a pair of combination mounting feet and electrical terminals 12 and 14. The terminals are of L-shaped configuration respectively having integral legs 16 and 18 spaced apart in a support device or stack 20 including layers of suitable insulating material designated by the numerals 21,

3,359,389 Patented Dec. 19, 1967 ICC 22 and 23. Adjacent the stack 20 is a stationary contact 24 which is fixed to an outwardly projecting portion 25 of the terminal leg 16. A plurality of elongated metal strips extend outwardly from the stack 20 in the same general direction as the projecting portion 25. Each of the strips are spaced from one another and cantilever supported at one end in the insulating stack 20 which is firmly fastened together such as by rivets 26, 28, it being understood that the rivets are received in enlarged holes in the stack 20 to prevent the rivets from establishing an electrical connection across the terminals 12, 14. More specifically, a flexible bimetallic actuator or bimetal 30 is provided with its fixed end positioned at the top of the stack 20 and insulated from the electrical terminal 12. Projecting outwardly from the bottom of the stack 20 is a base plate 32 having an adjustable stop screw 34 engaging the free end of an overlying support plate 36. The support plate 36 and the base plate 32 have fixed ends positioned in the stack 20 in electrical contact with opposite sides of the terminal leg 18. The base plate 32 may be formed of a suitable bimetallic material so that the stop screw 34 will exert a desired preselected force on the free end of the support plate 36 under varying ambient conditions.

To electrically connect terminals 12 and 14, a switch arm 38 of suitable resilient conductive material is centrally mounted upon a fulcrum abutment 40 formed to project upwardly from the support plate 36, and a second contact 42 is carried on an inner end of the switch arm 38 for cooperating with the stationary contact 24. It will be understood that the switch arm 38 has a pair of longitudinal slots intermediate its ends forming a pair of elongated strips as at 44 on opposite sides of a longitudinally extending center strip 46. In the specific illustrated embodiment, the center strip 46 is fixed to the abutment 40 and each side strip 44 is crimped such as at 4-8. This provides a permanent set in the switch arm 38 biasing its outer end upwardly of the abutment 40 and into engagement with a downwardly projecting tip 50 of a calibrating screw 52 mounted on the free end of the bimetal 30. For illustrative purposes, the contacts 24, 42. are shown in FIG. 1 as being in normally closed position and are adapted to be snapped into an open position shown in FIG. 2 in response to downward movement of the outer end of the switch arm 38.

The switch arm 38 is actuated by the bimetal 30 which in the preferred embodiment is controlled by a heater coil, not shown, wound around the bimetal and encapsulated within a covering 54 of suitable insulating material. It will be understood that the heater coil is suitably connected in a well known manner to a source of power, not shown. The low expansion side of the bimetal 30 faces downwardly toward the switch arm 38 whereby upon energizing the heater coil, the bimetal 30 gradually deflects downwardly. This causes the screw 52 to apply an increasing force on the outer end of the switch arm 38 in opposition to the force effected thereon by the abutment 40. As the bimetal moves downwardly, the outer end of the switch arm 38 is gradually deflected until its inner end suddenly snaps into engagement with the support plate 36 to break the electrical connection between the terminals 12 and 14.

In the event the contacts 24, 42 are sticking and fail to open in response to the snap action of the switch arm 38, an additional force is exerted on its inner end in a I contact opening direction in accordance with this invenportion of the disconnect lever 56 is provided with an opening 58 through which the screw 52 projects downwardly from the bimetal 30 into engagement with the outer end portion of the switch arm 38.

Toprovide an amplified force which is of substantially greater magnitude than the deflecting force exerted by the free end of the bimetal 30, a finger 60 is formed integral with the disconnect lever 56 to project downwardly toward the switch arm 38 adjacent its contact 42. The finger 60 of the disconnect lever 56 is suitably dimensioned such that under normal operating conditions the lower end of the finger 60 will be spaced slightly above the switch arm 38 when the bimetal 30 reaches its first deflected position shown in FIG. 2. If the snap action of the switch arm 38 fails to disconnect the contacts 24, 42 after the initial deflection of the bimetal 30, its continued travel beyond its position shown in FIG. 2 will force an adjustable screw 62, shown mounted in the bimetal 30 adjacent its free end, into engagement with the free end of the disconnect lever 56. This forces the finger 60 downwardly into engagement with the switch arm 38 adjacent its contact 42, and the leverage thus obtained eflectively transmits a steadily increasing additional force to break open the contacts so as to prevent them from being permanently welded together by electrical overheating.

When the heating coil is de-energized, the bimetal 30 contracts to disengage the adjustable screw 62 from the disconnect lever 56 which is then released to return to its normal position. Upon further upward movement of the bimetal 30, contact 42 snaps back into engagement with the stationary contact 24 under the bias of the resilient switch arm 38 thereby to again establish the electrical connection between the terminals 12 and 14.

Because of the inherent snap action of the resilient switch arm 38, the switch will function without chatter on either stepped or gradual power changes to effect switching of high current loads. The relative forces exerted on the switch arm 38 by the abutment 40 and the tip 50 of screw 52 provide a relatively small contact opening force which may be adjusted in accordance with a particular application, e.g., by adjusting the screws 34 and 52. The adjustable screw 62 maythen be set so as to engage the disconnect lever 56 when required to break the contacts which have become tacked together.

The positive disconnect feature incorporated in the switch of this invention significantly increases the probability of proper contact openingwhile at the same time retaining the quick, chatter-free switching action of a snap switch for use under high amperage conditions. In addition, the above described device is quick and easy to adjust in accordance with the varying operating conditions and may be conveniently manufactured and assembled at low cost to provide a durable, compact switch unit.

As will be apparent to persons skilled in the art, various modifications and adaptations of the structure above described wil become readily apparent without departure from the spirit and scope of the invention, the scope of which is defined in the appended claims.

'[ claim:

1. A bimetal actuated switch comprising a support having a fixed contact secured thereto, a switch arm mounted for movement relative to said support and carrying a second contact for movement toward said fixed contact, means mounting said switch arm on said support, a bimetallic member and a disconnect lever respectively cantilever supported on said support to extend therefrom in substantially parallel directions with said disconnect lever being positioned in spaced aligned relation between said bimetallic member and said switch arm, said bimetallic member and said disconnect lever having adjacent free end portions spaced apart from said support, said free end portion of said bimetallic member being movable to a first position for exerting an initial force on said switch arm remote from said second contact to initiate movement thereof away from said fixed contact, said bimetallic member engaging said disconnect lever upon continued movement beyond said first position, said disconnect lever having positive disconnect means for engaging said switch arm adjacent said second contact responsive to said continued movement of said bimetallic member to apply an additional contact opening force on said switch arm adjacent said second contact which force is of amplified magnitude relative to said initial force exerted on said switch arm.

2. The switch of claim 1 wherein said switch arm is contoured to provide snap action movement of said second contact toward and away from said fixed contact.

3. The switch of claim 1 wherein said positive disconnect means comprises an integral finger formed on said disconnect lever intermediate its opposite ends and adjacent said second contact on said switch arm, said finger projecting toward said switch arm in a contact opening direction for applying said additional contact opening force thereon.

4. The switch of claim 1 including adjustable means mounted on said free end portion of one of said disconnect lever and bimetallic members, said adjustable means projecting toward the free end portion of the other of said disconnect lever and bimetallic members for selectively initiating movement of said disconnect lever responsive to predetermined movement of said bimetallic member in accordance with different operating conditions.

5. A bimetal actuated switch comprising a support having a fixed contact secured thereto, a switch arm, mounting means connected to said support for mounting said switch arm, said switch arm carrying a second contact for movement toward and away from said fixed contact, a bimetallic member cantilever supported on said support and having a free end portion movable to a first position for exerting an initial force on said switch arm remote from said second contact to initiate movement thereof away from said fixed contact, a lever arm mounted on said support between said bimetallic member and said switch arm, said lever arm having a free end portion engageable with said free end portion of said bimetallic member and an integral finger located adjacent said second contact intermediate opposite ends of said lever arm, said finger projecting toward said switch arm in a contact opening direction for applying an additional contact opening force on said switch arm at a point adjacent said second contact tending to move the same away from said fixed contact in response to continued movement of said bimetallic member beyond its said first position, and adjustable means mounted on said free end portion of one of said lever arm and bimetallic members, said adjustable means projecting toward the free end portion of the other of said lever arm and bimetallic members to initiate movement of said lever arm whereby the actuation of said switch arm by said finger may be preset in accordance with different operating conditions.

References Cited UNITED STATES PATENTS 2,361,712 10/ 1944 Stouges. 2,658,975 11/ 1953 Zuckerman 2 200122 FOREIGN PATENTS 844,611 4/1939 France.

B'ERNARD A G'ILHEANY, Primary Examiner. H. A. LEWI'ITER, Assistant Examiner. 

1. A BIMETAL ACTUATED SWITCH COMPRISING A SUPPORT HAVING A FIXED CONTACT SECURED THERETO, A SWITCH ARM MOUNTED FOR MOVEMENT RELATIVE TO SAID SUPPORT AND CARRYING A SECOND CONTACT FOR MOVEMENT TOWARD SAID FIXED CONTACT, MEANS MOUNTING SAID SWITCH ARM ON SAID SUPPORT, A BIMETALLIC MEMBER AND A DISCONNECT LEVER RESPECTIVELY CANTILEVER SUPPORTED ON SAID SUPPORT TO EXTEND THEREFROM IN SUBSTANTIALLY PARALLEL DIRECTIONS WITH SAID DISCONNECT LEVER BEING POSITIONED IN SPACED ALIGNED RELATION BETWEEN SAID BIMETALLIC MEMBER AND SAID SWITCH ARM, SAID BIMETALLIC MEMBER AND SAID DISCONNECT LEVER HAVING ADJACENT FREE END PORTIONS SPACED APART FROM SAID SUPPORT, SAID FREE END PORTION OF SAID BIMETALLIC MEMBER BEING MOVABLE TO A FIRST POSITION FOR EXERTING AN INITIAL FORCE ON SAID 